Antiflutter device



April 5, 1938. D. c. ROWE, 2,113,000

ANTIFLUTTER DEVICE Filed May 17, 1933- INVENTOR. DONALD C ROWE.

Patented Apr. 5, 1938 um'rsn STATES PATENT OFFICE Donald C. Rowe, Kenmore, N. Y., assignor, by

mesne assignments, to Curtiss-Wright Corporation, a corporation of New York Application May 1'7, 1933, Serial No. 671,470

17 Claims.

This invention relates to aircraft, and particularly. to means for overcoming inadvertent flutter in control surfaces thereof.

In the recent development of high speed aircraft, a phenomenon commonly known as "flutter has sometimes appeared in the .control air- A foils, such as ailerons, rudder and/or elevators. The effect of flutter is to impose severe stresses on the aircraft structure with possible failure 13 resulting, and may also have the efiect of impairing the controllability of the aircraft. The

forward of its pivot axis, and eliminating slack and lost motion in the airfoil hinges and actuating members.

The subject invention provides. fully automatic means for damping and eliminating control airfoil flutter, and comprises briefly an auxiliary airfoil hinged to the control airfoil rearwardly. of 25 the control airfoil pivot. The auiliary airfoilis arranged with its center of gravity forward of its hinge axis, and with its center of pressure rearward thereof, which, in action, providesdamping moments for the control airfoil in a manner to be 30 more fully described hereinafter.

A somewhat similar and related phenomenon to control surface flutter is the vibration in flight of exposed brace wires and long exposed=-struts. The invention also provides means for damping vibration in such members.

Objects of the invention are to provide means for eliminating control airfoil flutter; to provide a freely swingable auxiliary airfoil hinged to a,

control airfoil; to provide a hinged airfoil hav- 49 ing its center of gravity forward of the hinge axis; to provide a hinged airfoil having the major part of its air contacting surface rearward of its hinge axis; and to provide an airfoil.- which 'by its inertia, tends to damp fluttering tendencies.

either fixed to or hinged to other aircraft menibers which may besubject to vibration or flutter,

to damp and eliminate such vibration or flutter.

In such auxiliary airfoils, the principles are iden- I 50 tical with the airfoils as applied to control sur-- 55 Further objects will be apparent in reading Some of these" Related ,objects are to provide auxiliary airfoil s,

the annexed specification and claims, and in considering the drawing, in which similar numbers designate similar parts, and in which:

Fig. 1 is a. side elevation of 'the empennage of an airplane embodying the invention,

Fig. 2 is an enlarged section on the line 2-2 of Fig. '1, showing, in dotted lines certain of the elements in different positions of adjustment,

Fig. 3 is a cross section througha brace wire having an auxiliary airfoil attached thereto, and 0 Fig. 4 is a cross section through a streamline strut having an auxiliary airfoil attached thereto. v

Describing the invention in detail, In is an airplane fuselage having a vertical fin H, and a horizontal stabilizer l2. At the trailing edge-of the fin II, a rudder I3 is pivoted, as at M, for swinging movement subject to the action of conventional rudder controls 15. The line a --a designates the rudder. pivot axis, which may be rear- 0 ward of the leading edge l6 of the rudder, or

may be at any other convenient location with respect to said leading, edge. Suitable brackets ii, attached to'the. fin I I, carry the rudder pivots.

Toward the trailing edge I8 of the rudder l3, a cutout I9 is made, and hinges are arranged on an axis b-b to carry'an'anxiliary airfoil 2i. Said airfoil 2| extends rearwardly from the hinge axis 17-17, and is freely swingable to either side of the plane of symmetry of the rudder l3. Itwill be noted-that, since the bulk of the surface of the airfoil 2! is rearward of the axis b--b, the center of pressure of air acting thereon will likewise be rearward of said axis, To place the center of gravity of the structure of. the airfoil -2l forward, of said hinge axis b--b, an arm 22, carrying a weight 23 at its forward encLextends for wardly-of the axis b-b, and is rigidly attached to the airfoil 2|? Alternative means will be apparent to thoseskilled in the art for carrying the center of gravity of the airfoil 2| forward'of the hinge axis b--b. v

The operation of the devicemay be more readily understood by referring to Fig. 2. The position C shows the rudder l3 and the auxiliary airfoil 2| 5 in alinement, which would be their normal position. Should the'rudder to flutter, that-is, be moved by forces othenthan those imposed-by the pilot of the'aircraft onthe controls liitj will movequickly to some displaced position such as D. When this occurs, the surface of the auxiliaryairfoil 2! will tend to be displaced at a greater anglethan the rudder; due to the weight of saidairfoil acting forward of the axis b-b,

which weight, by inertia resists displacement.. f

"ject to twist. Hera the airfoil 29' isswivelledto move it back to the plane of symmetry or to position C. -As such movement occurs, the rud- "der It and airfoil 2| will assume a position such -as E, wherein the rudder is moving'toward the plane of symmetry, but theairfoil 2| has, by its inertia, moved in oppodte angular sense to the rudder, since the center of gravity thereof is forward of its hinge axis. Hence, the air stream then acts on the opposite side of the airfoil 2|,

counteracting in some degree the restoring tuming moment initiated in position D, thus damping movement of both the rudder i3 and the airfoil 2|, preventing repetitious oscillation of either, and gradually returning both, their positions in the aircraft plane of symme The proportionate size, ity location and center of pressure location of the airfoil 2| will govern its effectiveness in damping flutter oscillation. The above X ctional descripweight, center ,0: gravtion is predicated upon correct roportions in the I device, which proportions may be evolved by cal culation and experiment. It will be readily appreciated that the structure and functions above described may be applied with identical effect to elevators, ailerons, brace'wires, struts or other movable aircraft members. In Fig. 1 the elevator 25, carried by the stabilizer l2, for instance, may be equipped with an auxiliary airfoil 2|; an arm 22' and a weight 23', to act in-the same manner as the similar elements 2|,'22 and 23.

The airfoil 2| as above described, may be either freely swingable to fulfill an anti-flutter function only, or may be controllable. Fig. 2 shows, in

dotted lines, one arrangement for controlling the airfoil 2|, wherein a horn 24, fixed to the airfoil, is connected by the rod 25 to a lever 26, movable on the axis a--a. I'his lever may in turn be controlled by a rod 21 leading to the pilot's "quarters, whereby the pilot may set the airfoil 2| I at an angle with respect to the rudder l3 for trimming yawing tendencies in the flight of the aircraft. Whether controllable or freely swingable, the airfoil 2| will have the desired effect in controlling flutter. When controllable, the

control elements, as 24, 25, 26 and 21 will have sufllcient resilience to allow the airfoil 2| to move sufliciently to damp flutter.

Figs. 3 and 4 show the anti-flutter or antivibration devices as they may be applied to streamline brace wires onstruts. In Fig. 3, a wire 28 has attached theretoa small airfoil-2S having a main ,portion 31 of light material extending principally rearwardly of the wire 28. so that .its center of surface area is rearward of the wire. A' nose ll of heavier material forms the forward portion ofthe airfoil 20, whereby the center of gravity of the unit is thrown forward of the center of the wire 28. If the wire starts to move crosswise ofthe airstream, the nose 2| lags by inertia, tilting the airfoil 28 and twisting the wire 28 to steer the unit. to a neutral position. In Fig. 4, the element 28' may represent a strut or the like which is relatively rigid and not subon the strut as at 32L so that as the element 28' moves crosswise, the airfoil.29' will turn about the swivel 32,- by the inertia of the nose it, and steer the strut 2l' back to a neutral position.

While I have described my invention in detail in its present preferred embodiment, it will be obvious to those skilled in the art, after understand- 1 ing my invention, that various changes and modifications may bemade'therein without departing from the spirit or scope thereof. I aim iii the appendedolaims Iclaimss'my invention:

1. ,In aircraft having a cont l airfoil "movable about a pivot, an auxiliary airfoil freely movable about a hinge carried-on said control airfoil, said auxiliary airfoil having its center of gravity forward 0: its-hinge and its center'of pressure rearward thereof.

2. In aircraft having a control airfoil controllably movable with respect thereto, an aux iliary airfoil hinged toward the rearward edge of said control airfoil movable with and with respect thereto, having its center of gravity forward of said hinge and its center of pressure rearward of saidhinge. g

3. In aircraft having a control airfoil subject to controlled movement, means for overcoming uncon'trolled flutter of said airfoil comprising a statically unbalanced auxiliary airfoil hinged to said control airfoil jhaving its center of 'avity forward of said hinge and its center of pr ssure rearward thereof.

4. In aircraft, a control airfoil pivoted thereto and extending rearwardly from the pivot, an auxiliary airfoil hinged toward its forward edge to said control airfoil, the hinge axis being spaced rearwardly from said pivot, and an arm extending from said auxiliary airfoil forward of said hinge, the mass of said arm being of a magnitude to-more thancounterbalance the weight of said auxiliary airfoil rearward of said hinge.

5. .In aircraft, a vertical rudder pivoted thereto, and an auxiliary airfoil hinged to said rudder rearwardly of said rudder pivot for free swinging with respect thereto, said airfoil having its center of gravity forward of said hinge and its center of pressure rearward of said hinge.

6. In aircraft, an elevator pivoted-thereto and .an auxiliary airfoil hinged to said elevator rearwardly of said elevator pivot for free swinging with respect thereto, said airfoil having its center of gravity forward of said hinge, and center of p'ressure rearward of said hinge.-

7. In aircraft having a member subject to both controlled anduncontrolled relative movement in flight, an auxiliary airfoil for damping the uncontrolled movement attachedto said member, said airfoil having its center of pressure rearto cover all such modifications and movement comprising an element attached thereto intermediate the width of said ele'ment, said element having its aerodynamic center of .pressure rearward of said point of attachment, and having a mass forward of said pointof attachment greater than the mass rearward thereofi I 9.In ircraft, aj movable element'in the slipstream nd an auxiliary airfoil embracing said element having its aerodynamic center of pressure rearward of'its Point of; tiMT hment to said element, and having means fofie'stablishing thecenter of gravity theeof. forward oi' said point of attachment. ff f 10. In aircraft, an auxiliary airfoil, 'and a movable member in'th'e slipstream embraced by. and attached tos'aid airfoil,; d 'airioil having 1th center of pressure rearward' ofthe point of ward of its point of attachment, and having 20 ment exposed to the airstream, means for preattachment and having its center ward thereof. 1 I g I 11. In aircraft having a member subject to uncontrolled relative movement'in flight, an auxiliary airfoil for damping said movement controlled in its own movanent only by its response to airflow and inertia, pivoted to swing freely on and with respect to said member, said airfoil having its center of pressure rearward of said pivot, and'having its center of gravity forward of said pivot. 1

12. In an aircraft element exposed to the airstreamand subject to movement aboutv an axis of oscillation, flutter'prev'ention means compris-.

ing an auxiliary control surface carried by said element, said surface having its center of pres--' sure rearward of the oscillation axis of said eleits center of pressurerearward of is. I a a rc eleme w i ment', and having its center of gravity forward-of said oscillation axis. 7 g

13. In a relatively long slender aircraft eleof gravity for-" g 3 trolled movement, meana for preventing flutter thereof, comprising an auxiliary airfoil carried thereby and disposed in the airstream, said airfoil being hinged to said element and having its centerof gravity forward of the hinge line, and its center of pressure rearward thereof.

15. In means for overcoming flutter in an aircraft element subject to controlled movement, an auxiliary airfoil mounted for oscillation on said element, said airfoil having its center of mass forward of the axis of oscillation, and having its center of pressure rearward of said axis of oscillation. v 16. In aircraft, an airfoil subject to controlled movement, an auxiliary anti-flutter airfoil hinged to said controlled airfoil, the center of gravity of said auxiliary airfoil being forward of said hinge and the center of pressure thereof bei rearward of said hinge.

17. In aircraft, a control airfoil pivoted thereto, and an auxiliary airfoil hinged to said control airfoil rearwardly of said control airfoil pivot for free swinging movement with respect to the control airfoil, said auxiliary airfoil having its center of gravity forward of said hinge and its center of pressure rearward of said hinge. 

